Synthetic rubber composition containing a fatty acid nitrile or polymer thereof and method of making the same



natural rubber.

Patented'Au'g'. 29, 1950 SYNTHETIC RUBBER COMPOSITION CON- TAINING A FATTY POLYMER THEREOF AND METHOD OF MAKING THE SAME ACID NITRILE OR Anderson w. Ralston and mm M. Corlcy, om-

cago, Iil., assignors to Armour and Company, Chicago, 111., a corporation of Illinois No Drawing. Continuation of application Serial No. 435,134, March 18, 1942. This application March 6, 1948, Serial No. 13,514

l 1! Claims. (Cl- 260-325) This invention relates to synthetic elastomers and it comprises synthetic elastomers containing high molecular weight aliphatic nitrile compounds, and processes for preparing the same; it further comprises synthetic elastomers containing nitriles combined with monomers of the type capable of forming elastomers on polymerization, the nitriles being those derived from fatty acids and having at least twelve carbon atoms.

The development of synthetic elastomers, such as so-called synthetic rubbers, has created many problems respecting ways of compounding such elastomers as well as ways of making them. In the early development of so-calledsynthetic rubber, efforts were made to reproduce natural rubber synthetically. In later years, however, it has been discovered that rubber-like polymers could be prepared which have characteristics quite different from ordinary natural rubber and that such characteristics or properties particularly suit these synthetic products for many uses to which rubber itself was not well adapted. For example, many of these synthetic elastomers have high oil resistance, much higher than that of Consequently, such synthetic products can be used in many relations where natural rubber is at a distinct disadvantage.

In order to form a useful rubber product, it

is necessary to admix with these elastomers sub- Plasticizers, softeners and the like have also been added to natural rubber, but the agents used with natural rubber are not in many instances adaptable for compounding synthetic rubbers.

We have now discovered a class of organic compdunds which are particularly useful in the compounding of synthetic elastomers. These compounds can be generally defined as aliphatic nitriles having at least .twelve carbon atoms. The nitriles which we use in the practice of our invention may be derived from fatty acids by processes now well known in the art. Such fatty acid nitriles can be either saturated or unsaturated, but preferably should be unsaturated. We desire to clearly distinguish our invention from the use of lower molecular weight nitriles, such as acrylonitrile. However, acrylonitrile, when copolymerized with butadiene, forms a synthetic elastomer to which our nitriles can be added in the compounding of such synthetic polymer.

Among the synthetic elastomers to which we can add aliphatic nitriles may be mentioned the following: butadiene polymers as such, usually made by polymerizing butadiene (having the structure CH2=CHCH=CH:) with sodium; butadiene co-polymers, such as those made by polymerizing a mixture of butadiene and styrene, or butadiene and acrylonitrlle; isoprene polymers; chloroprene polymers; polyisobutylene; and the like. Our nitriles can also be used for compounding those rubber-like products known as the Thiokols made from ethylene dichloride, or dichloroethyl ether, and sodium sulfides.

All of the above listed synthetic elastomers are substances having rubber-like characteristics although the elasticity may vary markedly and, in fact, can be controlled as desired.

In all instances the nitriles of our invention can be admixed with the synthetic elastomers in the compounding thereof to give articles of commerce.

The nitriles embraced within our invention are all those nitriles having twelve or more carbon atoms including that of the nitrile radical. Such nitriles are as follows: oleonitrile, linoleonitrile, linolenonitrile, eruconitrile, stearonitrile, lau'ronitrile, elaidonitrile, brassidonitrile, palmitoleonitrile, and mixtures thereof. Desirably, we can use mixtures of nitriles prepared from natural oils and fats such as fish oils, cottonseed oil, soya bean oil, lard, tallow, etc. In the list above given oleonitrile and linoleonitrile may be regarded as illustrative of the unsaturated fatty acid nitriles. We have discovered that all of thme nitriles are compatible with synthetic elastomers and that incorporating these nitriles in the elastomers aids markedly in the compounding thereof with sulfur, vulcanization accelerators, and the like. Indeed it is believed that these nitriles do more than merely modify the elastomer. Nitriles of the character specified undergo polymerization, and sulfur is a, polymerizing agent which will convert the nitriles to polymerized products. Thus, for example, a mixture of parts of a butadiene-styrene co-polymer with 25 parts of oleonitrile, together with sulfur and accelerators, gives a vulcanized product having soft, rubbery properties superior to that obtained when the butadiene-styrene co-polymer is vulcanized in the absence of the oleonitrile. We believe that the oleonitrile polymerizes to some extent in the presence of the sulfur and that the nitrile forms a kind of co-polymer with other constituents present.

Polymerized nitriles as such can be used to special advantage in the compounding of synthetic elastomers according to our invention. Such polymerized nitriles may be made by subjecting fatty acid nitriles to the action of polyv celerator.

3 merizing catalysts as fully described in the Ralston Patent 2,175,092.

The use of our nitrlles in compounding synthetic elastomers is particularly important from the point of view of economizing on the amount of elastomer in the final compound. This is because these nitriles, particularly the polymerized nitriles, act as extenders, thusenabling us to prepare satisfactory rubber-like products containing a smaller proportion of the elastomer than has hitherto been considered necessary.

For example, as much as 50% of an unsaturated nitrile. like linoleonitrile, can be admixed with v the synthetic elastomer to give a product which can be vulcanized as desired, yet the availability of the nitrile polymer, or unpolymerized fatty acid nitrile, is much greater than that of the'elastc mer, and the cost is much less. Also where our improved synthetic elastomers are used in combination with natural rubber, it is possible to use a smaller proportion of natural rubber than is necessary where our invention is not employed. ,We shall now give examples of ways of combining the nitriles of the preesnt invention with synthetic elastomers.

Example 1 100 parts of butadiene-styrene co-polymer o the Buna S type are milled with parts of oleonitrile, 5 parts of'sulfur, and 5 parts of zinc oxide, together with any suitable accelerator. This entire mass is thoroughly blended and then vulcanized in the usual way. The product has high water resistance, oil resistance, and resistance toabrasion.

To the butadiene-styrene co-polymer of Example l'we add, after incorporating the nitrile.

' from to parts by weight of carbon black and about 3 parts by weight of stearic acid. The resulting vulc'anizing mixture is suitable for tire treads.

Example 3 100 parts of a butadiene-acrylonitrile polymer classified as Buna N was mixed with 25 parts of Example 5 100 parts of polymerized chloroprene (2-chl robutadiene) was mixed with 15 parts of linoleonitrile. 5 parts of sulfur and a small amount of diphenyl guanidine. These ingredients were mixed together until the mixture became homogeneous. The mixture was then heated for one hour at 140 C. This resulted in a product having excellent elasticity and possessing many of the properties of a vulcanized natural rubber.

Example 6 natural rubber product.

Another important way of incorporating allphatic nitrlles derived from fatty acids in synthetic elastomers, is one in which the nitrile is incorporated with the elastomer during the procpolymerized nitriles, 5 parts of sulfur, 50 parts of carbon black, 3 parts of stearic acid anda small amount of accelerator. The polymerized nitriles were prepared from 1am fatty acid nitriles and were made by heating parts of lard fatty acid nitriles with 5 parts by weight of aluminum chloride for 17 hours at 0. They were washed several times with water and dried before use.

The mixture of polymerized butadiene-acrylonitrile with the polymerized nitriles and the other ingredients mentioned above was mixed until-the product became homogeneous. It was then heated to 140 C. for one hour. The product was a rubber-like substance, possessing elasticity and flexibility. It has many of the properties of ordinary vulcanizedrubber.

Example 4 elastierubber-like substance. It had many of ess of forming the latter. .Most of these synthetic compounds are prepared by polymerizing the polymerizable constituents while emulsified in water. For example, butadiene and styrene are emulsified in water containing a polymerization catalyst and then the mixture is subjected to polymerizing conditions, such as elevated temperature. Thereafter the c'o-polymer thus formed is separated from the emulsion by coagulation. In practicing this feature of our invention we emulsifythe nitrile along with the other constituents and polymerize the entire mixture in one step. Thus we avoid the necessity for separately milling or otherwise compounding the aliphatic nitriles with the elastomer. Moreover, we gain the benefits of a homogeneous coagulum in which we believe the nitrile is co-polymerized with other constituents.

For example, we emulsify about '70 parts by weight of butadiene, 30 parts by weight of styrene, or acrylonitrile. 4 parts by weight of an emulsifying agent, one-half part by weight of a, polymerizing catalyst, such as. hydrogen peroxide, sodium perborate, or otherperoxide, 0 parts by weight ofstearonitrile or oleonitrile, and 200 parts .by weight of water. This mixture is then given for purposes of explanation only and itis expected that many changes may be made therein and the procedures given may be varied to accommodate specific conditions of operation, all within the spirit of our invention.

This application is a continuation of our application Serial No. 435,134, filed March 18, 1942, now abandoned.

What we claim as new and desire to secure by Letters Patent is:

1. A process for preparing a synthetic elastomer composition comprising mixing a fatty acid nitrile of at least 12 carbon atoms with butadiene, and thereafter polymerizing the mixture to form a synthetic elastomer composition.

2. A process for preparing a, synthetic elastomer composition comprising mixing a fatty acid nitrile of at least 12 carbon atoms with butadiene and acrylonitrile, and thereafter polymerizing the mixture to form a synthetic elastomer composition.

3. A composition of matter comprising a synthetic rubber prepared by the polymerization of butadiene, and, as a softener therefor, a fatty acid nitrile containing at least 12 carbon atoms.

4. A composition of matter comprising a synthetic rubber prepared by the polymerization of butadiene and acrylonitrile, and, as a softener therefor, a fatty acid nitrile containing at least 12 carbon atoms.

5. A composition of matter comprising a synthetic rubber prepared by the polymerization of butadiene, and, as a softener therefor, an unsaturated fatty acid nitrile containing at least 12 carbon atoms.

6. A composition of matter comprising a synthetic rubber prepared by the polymerization of butadiene and acrylonitrile, and, as a softener therefor, an unsaturated fatty acid nitrile containing at least 12 carbon atoms.

7. A composition of matter comprising a synthetic elastomer prepared by the polymerization of butadiene and styrene, and, as a softener therefor, a fatty acid nitrile having at least 12 carbon atoms.

8. A composition of matter comprising synthetic rubber prepared by the polymerization of butadiene-1,3 and, as a softener therefor, 9-octadecene nitrile.

9. A composition of matter comprising a synthetic elastomer prepared by the polymerization of butadiene-1,3 and acrylonitrile and, as a softener therefor, Q-octadecene nitrile.

10. A synthetic elastomer prepared by the polymerization of a composition selected from the class consisting of butadiene polymers, isoprene polymers, chloroprene polymers, and polyisobutylene, said synthetic elastomer containing a fatty acid nitrile having at least 12 carbon atoms.

11. A composition as set forth in claim 10 wherein said composition is a vulcanized material.

12. A composition as set forth in claim 10 wherein said nitrile is unsaturated.

13. A composition as set forth in claim 10 wherein said nitrile is oleonitrile.

14. A process for preparing a synthetic elastomer composition comprising mixing a fatty acid nitrile of at least 12 carbon atoms, sulphur and a synthetic substance of the class consisting of butadiene elastomers, isoprene elastomers, chloroprene elastomers, and elastomeric polyisobutylene and heating the mixture to form a synthetic elastomer composition.

15. A process for preparing a synthetic elastomer composition comprising mixing a fatty acid nitrile having at least 12 carbon atoms with a substance selected from the class consisting of butadiene elastomers, isoprene elastomers, chloroprene elastomers, and elastomeric polyisobutylene and heating the mixture to form a synthetic elastomer composition.

16. A process for preparing a synthetic elastomer composition comprising mixing a-fatty acid nitrile of at least 12 carbon atoms with a monomer which is capable of polymerization to form synthetic elastomer substances of the class consisting of butadiene polymers, isoprene polymers, chloroprene polymers, and polyisobutylene, and thereafter polymerizing the mixture to form a synthetic elastomer composition.

17. A synthetic elastomer prepared by the polymerization of a composition selected from the class consisting of butadiene polymers, isoprene polymers, chloroprene polymers, and polyisobutylene, said synthetic elastomer containing a member selected from the group consisting of fatty acid nitriles having at least 12 carbon atoms and the polymers thereof.

ANDERSON w. RALSTON. HOYT M. CORLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Ralston Oct. 3, 1939 OTHER REFERENCES Number 

17. A SYNTHETIC ELASTOMER PREPARED BY THE POLYMERIZATION OF A COMPOSITION SELECTED FROM THE CLASS CONSISTING OF BUTADIENE POLYMERS, ISOPRENE POLYMERS, CHLOROPRENE POLYMERS, AND POLYIOSBUTYLENE, SAID SYNTHETIC ELASTOMER CONTAINING A MEMBER SELECTED FROM THE GROUP CONSISTING OF FATTY ACID NITRILES HAVING AT LEAST 12 CARBON ATOMS AND THE POLYMERS THEREOF. 